Project Summary/Abstract We present a substantially revised application in response to our reviewers' concerns. Major issues that were addressed include: (a) description and steps to accomplish planning activities; (b) standardization of rehabilitation treatments; (c) measurement of compliance and content of rehabilitation; (d) rehabilitation expertise of our team and ensuring a balance of surgical and non-surgical investigators; (e) outcome measures selection and follow-up duration; (f) assessment of willingness of patients to participate in a randomized trial; (g) sample size justification, and; (h) statistical analyses. Shoulder symptoms accounted for 11.5 million ambulatory care visits in 2010 in the United States. Rotator cuff tears are one of the leading causes of shoulder pain and disability, and accounted for an estimated 272,148 ambulatory surgeries in 2006. Despite the substantial public health and economic impact of rotator cuff tears and their treatments, there is lack of evidence on a head-to-head comparison of surgery versus non-operative treatment. The urgent need for research in this area and a well-designed randomized controlled clinical trial is highlighted by multiple authoritative agencies including the American Academy of Orthopaedic Surgeons (AAOS), Agency for Healthcare Research and Quality (AHRQ), and in Cochrane reviews. Our multi-disciplinary team is in a unique position to conduct a randomized controlled trial of operative versus non-operative treatments for atraumatic full-thickness rotator cuff tears in patients' ?50 years of age. We propose recruitment from six (6) high volume sites that form part of a large multi-center consortium called the Multicenter Orthopaedic Outcomes Network (MOON). Using this infrastructure, we propose to recruit 400 patients with atraumatic full-thickness rotator cuff tears and randomize them to either operative or non- operative treatments with the goal to compare pain and function in these two groups at one (1) year follow-up. We will also study effect modification by rotator cuff tear size and patient age. Prior to conducting such a large scale randomized trial, the U34 grant would provide us the needed funding to: (a) Draft a manual of operations and procedures (MOOP); (b) Finalize study questionnaires and forms; (c) Finalize operative and non-operative intervention standards of care; (d) Set up physical therapist referral database by zip code; (e) Obtain IRB approval from all trial sites; (f) Set up and test REDCap database for secure data storage and online randomization; (g) Train all site personnel to standardize recruitment, study procedures, and data collection, and; (h) Set up a data and safety monitoring board. During the U34, we will perform a pilot study to assess homogeneity and compliance with rehabilitation protocols, and validate patient self-report of rehabilitation frequency and compliance with clinical records. We will assess willingness of patients to participate in a randomized trial of operative versus non-operative treatment for rotator cuff tears. Thus, the U34 is critical to accomplish the subsequent randomized clinical trial.